For high definition television applications and multimedia applications, the repeaters mounted on board known communication satellites comprise multi-spot transmission and reception systems which are based on transparent architectures offering uplinks between one or more earth stations and the repeater and downlinks between the repeater and a plurality of users. Current architectures do not allow the implementation of direct links between the users, referred to as inter-spot links or mesh links, and impose a fixed connectivity between the spots of the users and the earth stations.
FIGS. 1a and 1b show an example of the architecture of a transmission and reception system of a current repeater, offering uplinks and downlinks respectively. The transmission and reception system providing the links between at least one earth station, also referred to as a hub, and users comprises at least one outbound section 45 corresponding to the transmission of signals transmitted by the earth station to users, and at least one return section 47 corresponding to the transmission of signals transmitted by users to the earth station. The number of outbound sections and return sections is equal to the number of earth stations deployed.
Each forward or outbound section, as shown schematically in the example in FIG. 1a, generally comprises a reception antenna 6 comprising a hub reception source dedicated to the reception of signals 5 originating from a single earth station. In the case where a plurality of earth stations are deployed, the reception antenna 6 comprises a plurality of hub reception sources 1 to N, where N is an integer greater than 1, each hub reception source being dedicated to the reception of signals originating from a single earth station. The signals received by a hub source, for example by the hub reception source 1, allow a plurality of user spots 14 to be served, each user spot 14, also referred to as a beam, corresponding to the coverage of a predetermined terrestrial geographical zone. The user spots are transmitted by one or more user transmission antennas 7. For example, four user transmission antennas are shown in FIG. 1a. The radio frequency signals transmitted by an earth station generally occupy a broad frequency band. These hub signals 5 are received by a transmission channel linked, for example, to the hub reception source 1 of the hub reception antenna 6. The broadband signals received pass through a filter 11 which enables the useful hub reception frequency band RX to be filtered, and then through a low noise amplifier 12, and are frequency-transposed by one or more frequency converters 13 to pass from the hub reception frequency band RX to the user transmission frequency band TX. The frequency band allocated to the user spots 14 being generally narrower than the band allocated to the earth stations, the use of a plurality of frequency converters 13 furthermore allows the transmission band to be doubled up, i.e. it allows frequency bands which were disjointed on reception to be brought back to the same central transmission frequency. This is generally necessary to occupy a transmission frequency band that is generally narrower than the reception band. It is thus possible to occupy a transmission band that is twice as narrow as the reception band, or even more depending on requirements. The number of converters used is therefore equal to the ratio between the width of the hub reception band RX and the width of the user transmission band TX. In this example, following amplification, a divider 15 implements a division by two of the power of the signal and the two signals resulting from the division are frequency-transposed by two frequency converters 13 which, as shown in FIG. 2a, allow the received frequency band to be split into two bands which, following frequency conversion 13, will be centred on the same frequency and will be twice as narrow as the received frequency band. The signals whose frequencies correspond to the two transmission frequency bands thus constituted are then transmitted respectively to two input demultiplexers IMUX 16 (Input Multiplexer) which split them into a plurality of contiguous sub-bands, each sub-band having a fixed width and being adjustable, for example on the ground, according to transmission frequency requirements. Through these successive stages described above, four independent transmission sub-bands Uj, . . . , Uj+3, are thus constituted on the basis of a single broadband reception and are shown in the example in FIG. 1a. Each of these transmission sub-bands is dedicated to the transmission of radio frequency signals to a predetermined user spot 14. A colour code is generally allocated to each sub-band to represent the transmission frequency sub-bands transmitted to the user spots 14. This colour code defines the resources used. Each colour therefore corresponds to a frequency resource defined by the central frequency of the frequency band of the signal. In the case of FIG. 2a, eight user transmission frequency sub-bands TX are generated on the basis of the reception of a hub band RX originating from a hub spot 5. Following frequency transposition 13, certain sub-bands are at the same central frequency and are allocated the same colour even though each of the sub-bands is intended for different user spots 14. In this example, the eight user transmission frequency sub-bands TX generate four different colours, each colour therefore being used twice. Each transmission frequency sub-band (or colour) is then amplified by a pre-amplifier 17 then by a progressive wave tube 18 followed by a filter 19 which implement a power amplification and a filtering of the non-linearities so that the user sources 20 only transmit the useful frequency spectrum to the user spots 14.
Each return or inbound section 47, as shown schematically in the example in FIG. 1b, is inverted in relation to the outbound section and comprises reception user sources 21, each intended to receive radio frequency signals in a narrow reception frequency band and able to transmit the received signals to a receiving earth station. In the case of the use of antennas operating on transmission and reception, the reception user sources 21 are the same as the transmission user sources 20 of the outbound section. The reception user sources 21 are each connected respectively to a filter 22 followed by a gain control low noise amplifier 23 which enables control of the respective levels received on each user reception channel Uj, . . . , Uj+3 corresponding to each source 21. Following amplification, the signals received in the contiguous frequency sub-bands Uj, . . . , Uj+3 are recombined by input multiplexers IMUX 24 to reconstruct a broader-band frequency spectrum, and are then transposed into the transmission frequency band TX by one or more frequency converters 25. The signals from the frequency converters 25 are recombined by a signal combiner 26 to reconstitute the total band allocated to the earth station, as shown in FIG. 2b, and to transmit, after amplification in the channel amplifiers 27 and power amplifiers 28 and after filtering 29, the different signals from the user antennas 7 to the earth station by a dedicated hub transmission source of the hub antenna 6, whereby the hub transmission sources may be the same as the hub reception sources 1 to N in the case of the use of transmission and reception antennas.
This type of architecture only allows the provision of uplinks and downlinks between earth stations and user spots and does not allow the implementation of direct inter-spot links between users. To implement inter-spot links, it is known, as shown in the architecture example in FIG. 3, for the repeater to be equipped with an additional link section, referred to as the mesh section, which is intended to provide inter-spot links only, the mesh section comprising a digital transparent processor (DTP) 31. The DTP 31 comprises input access points 32, each dedicated to the reception of signals originating from a first user spot 14 and output access points 33, each dedicated to the retransmission of the received signals to a second destination user spot 43. Each input access point 32 of the DTP 31 is connected to a signal reception source 36 via a dedicated reception frequency conversion channel, and each output access point of the DTP 31 is connected to a radio frequency signal transmission source 37 via a dedicated transmission frequency conversion channel. In each reception frequency conversion channel, the signals received by each reception source 36 are previously filtered by a filter 34 and amplified in a low noise amplifier 35 then frequency-converted in a converter 38. The DTP 31 implements a fine digital filtering which enables the division of the frequency bands of the received signals originating from each user spot into a plurality of sub-bands with narrower widths, each sub-band resulting from the division being dedicated to a single user, and implements a routing of each sub-band then a reorganisation of said sub-bands in such a way as to reconstitute the bands dedicated to each destination user spot 43, the reorganised bands being respectively delivered to the output access points 33 of the DTP 31 and transmitted on the corresponding transmission frequency conversion channels. Following frequency conversion 39 then amplification 40, 41 and filtering 42, the transmission sources 37 connected to each transmission frequency conversion channel retransmit the signals to the destination user spots 43.
However, the processing capacities of a DTP 31 are limited in terms of bandwidth that can be processed per access point and in terms of total processing capacity corresponding to the product of the capacity per access point times the number of access points 32, 33 of the DTP. These limitations do not permit the processing of a large number of connections between the spots 36 to be retransmitted and the destination spots 43. Currently, the processing capacity of a DTP is in the order of 2000 MHz, the capacity per access point is 250 MHz and the number of access points of the DTP is limited to eight user spots in total, whereas the typical service requirements for a payload are twenty-four user spots. To increase the processing capacity of the DTP 31, it is possible to limit the frequency band of each access point, for example to 50 MHz, but this multiplies the number of frequency conversion channels on either side of the DTP 31. For example, in the case of 80 user spots, 160 frequency conversion channels are necessary, which increases the complexity of the architecture around the DTP 31, the number of conversion channels on either side of the DTP and the DTP itself.